1. Field of the Invention
The present invention relates generally to mariculture, and, more particularly, to a method for inducing planktonic bivalves to set on a substrate.
Oysters, mussels, clams, scallops and the like are referred to as bivalves, and the commercial farming of such bivalves is referred to as bivalve culture. All bivalves have a similar life cycle. Initially, the bivalve larvae are free swimming ("planktonic"). After a time, the planktonic larvae develop into a stage capable of crawling referred to as a pediveliger. Pediveligers which are capable of attaching to a substrate (referred to as "setting") are said to be competent. After setting on a substrate, such as rocks, sticks, aged adult shells and the like (referred to as "cultch"), the larvae are allowed to develop and are finally harvested when they reach a suitable size. The expansion of the bivalve culture industry has been limited by the lack of an effective method of replacing population lost through harvest and mortality with new larvae. In part, this is due to a inability to effectively induce competent pediveligers to set on a desired substrate such as cultch in an artificially maintained setting tank.
The oyster industry has developed a method for allowing the setting of hatchery-reared competent pediveligers onto cultch. The technique involves placing the competent pediveligers into a tank filled with seawater and containing cultch. The pediveligers are allowed to set on the cultch, under controlled temperature conditions, for a time sufficient to achieve the desired number of larvae attached to the cultch. This method, although functional, requires seeding a very large number of larvae in the setting tank because of the inherently low percentage of larvae which set. Moreover, the method requires that the seed larvae have already reached the competency stage prior to seeding, or that the period of time in the tank be increased until they reach such stage, in order for setting to occur. A final shortcoming of the prior art is that the cultch must be of a certain type which presents the proper tactile stimuli to the pediveligers to induce setting thereon. It is, therefore, desirable that a method be found to induce bivalve larvae to set on a wide variety of substrates at a relatively high percentage of set within a relatively short period of time.
2 Description of the Prior Art
Veitch and Hidu in an article entitled Gregarious Setting in the American Oyster Crassostrea virginica Gmelin: I. Properties of a Partially Purified "Setting Factor", Chesapeake Science, Vol. 12, No. 3, p. 173-178 (Sept. 1971) identified four molecules (tyrosine, thyroxine, 3, 5-diiodotyrosine, and 3-iodotyrosine), separated from a conjugate protein found in oyster shell liquor, which were found to promote setting of planktonic oyster larvae. In testing the effects of these molecules on pediveligers, the results were statistically significant, but addition of the complete conjugate protein was much more effective in enhancing the setting response than any of the molecules tested individually. They concluded that the gregarious setting factor was the complete thyroprotein with a molecular weight in excess of 100,000 Daltons.